It is often necessary to couple together the end of a pipe, such as a water pipe, to another member, such as another pipe, a valve, a fitting, or other similar pipe-like structure. In some cases, the ends of two adjacent pipes may be flanged, and the flanges can be placed into confronting relationship to facilitate bolting the pipes together. This coupling arrangement, however, is not always feasible or available.
A coupling device known as a mechanical joint, or MJ, can be used where one of the pipes does not have an available flanged end. In that situation, the end of the non-flanged pipe is telescopingly received into a flared end of a flanged member, with a following ring or annular gland situated over the pipe adjacent to the flange. A gasket is provided which compresses into the pipe surface and against the flare of the other member to create a water-tight seal as the follower ring is bolted to the flange.
Mechanical joints are suitable for a number of situations, but may not be able to retain the water-tight connection between the pipes where the pipes are subjected to hydraulic thrust forces which might tend to cause the pipes to telescope apart. To reduce the risk of the pipes coming apart, pipe joint restraints have been provided with the MJ or in lieu thereof. A pipe joint restraint typically has an annular retainer gland defining a pipe-receiving space therethrough and having an axial centerline. One or more pockets are associated with the annular retaining gland and have an open end confronting the pipe-receiving space and a top wall radially outwardly of the opening. A gripping element or wedge is movably supported in the pocket and has a gripping edge, such as a tooth, to frictionally engage the pipe surface when the gripping element is moved to project out of the pocket toward a pipe in the pipe-receiving space. The gripping edge resists the tendency of the pipe to move away from the other member when the gland is bolted to the flange of the other member.
Conventionally, the frictional engagement of the wedges to the pipe surface resists separation of the pipe and the joined member. However, reliance on friction as the primary mechanism to hold the pipes together imposes significant requirements on the pipe joint restraint which can be difficult to achieve in the field. By way of example, the gripping element is moved into engagement with the pipe by a threaded bolt in operative engagement with the wedge and the pocket such that as the bolt is rotated, the wedge can be moved into the pipe surface. In order to provide a sufficient hold to the pipe, however, it has been required to tighten the bolt to relatively high torques, typically greater than about 65 to 75 or 90 foot-pounds for ductile iron pipes. These high torques require more effort and exertion by the personnel who install or service the pipes. These difficulties are compounded when personnel must install pipes in the often inhospitable conditions of the outdoors, such as freezing, wet, or muddy conditions, and in the tight spaces often experienced in the field. Moreover, application of such high torques can deflect the pipe, making it difficult to maintain a seal. Often, the axial bolts that secure the gland to the flange on the adjoining member must be re-tightened to maintain a good seal. Moreover, the thrust forces may exceed the frictional ability of the joint to resist separation of the pipe and the joined member.
Because piping systems may be formed from many different materials such as metals (like ductile iron or steel, for example) or polymeric materials such as polyvinyl chloride (PVC) or other plastic materials, and because each of these materials exhibits different properties and characteristics, different types of wedges are required to adapt pipe joint restraints for use with each of the different types of pipes. For example, pipes formed from ductile iron are much harder than pipes formed from polymeric materials, such as PVC. Accordingly, the surface areas contacted by the wedges, as well as the number of wedges and the particular configuration of the gripping edges, may be considerably different depending on the material from which the pipe is formed. In addition, the torque required to sufficiently secure the wedges to the respective types of pipes varies due to the differences in material properties of the pipes. Because pipes are also available in different sizes, further variation in the configuration of the wedges is required to accommodate different sizes of pipe. To accommodate all of these various configurations, manufacturers or suppliers must maintain a considerable inventory of different configurations of wedges and retainer glands, as well as the tooling needed to produce these various configurations. Service and installation personnel might also have to keep on hand several different types of retainer glands and corresponding wedges to be able to work with the many different variations of pipes that may be encountered in the field.